Method of inhibiting metal corrosion

ABSTRACT

A method of inhibiting metal corrosion is applicable to a metal-containing substrate, which has a surface in contact with a reaction solution. The method includes the steps of mixing ozone with the reaction solution and forming a metal oxide protective layer on the surface of the metal-containing substrate, so as to prevent metal beneath the protective layer from being continuously oxidized and corroded. In the method, the reaction solution contacting with metal is further adjusted in its oxidation-reduction property and pH value to change the corrosivity of the reaction solution and mitigate the corrosion tendency of metal.

FIELD OF THE INVENTION

The present invention relates to a method of inhibiting metal corrosion, and more particularly to a method applicable to precision electronic devices to inhibit metal corrosion thereof.

BACKGROUND OF THE INVENTION

Metal materials are widely applied in different industrial fields. Precision devices, such as semiconductor electronic elements and photoelectric displays, all have lead wires made of metal materials, including aluminum (Al), copper (Cu), molybdenum (Mo), chromium (Cr), titanium (Ti), etc. In the process of manufacturing the devices, these metal materials are corroded due to contacting with chemical agents and water of different temperatures and pH values being used in relevant processes, such as photolithographing, stripping, etching, washing, etc. The corroded metal materials would adversely affect the product quality.

A metal material is corroded because a cell reaction, or electrically polarized oxidation-reduction reaction, occurs between the metal and the substances existed in the environment in which the metal is processed, and the metal loses electrons and is corroded in an anodic oxidation reaction. There are different ways of protecting metal material against corrosion, including coating the metal material to isolate the same from a corrosive environment, and adding a corrosion inhibitor to change the corrosivity of the environment in which the metal material exists.

By “coating”, it means to form a layer of appropriate organic compound, such as a cyclic polymer, or a metal protective layer on the metal material, so as to isolate the metal material from a corrosive environment or minimize the area of the metal material exposed to the corrosive environment, and thereby reduce the possibility of corrosion of the metal material. The metal protective layer is normally used as a sacrificial anode, so that the relatively active metal protective layer instead of the metal lead wire is consumed in the reaction.

In another way of protecting metal material, a corrosion inhibitor is added into an environment in which the metal material is processed, so as to change the corrosivity of the processing environment and reduce the metal corrosion. Some examples of this way include reducing the dissolved oxygen in water, and adjusting the pH value of the water, so as to lower the oxidation and accordingly, the corrosion of metal material.

However, most of the chemical agents used to inhibit corrosion are toxic or non-biodegradable to have adverse influences on the environment. Therefore, it is an important issue among different industrial fields to develop a method of inhibiting metal corrosion to maintain good electrical performance for metal lead wire and protect the environment at the same time.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a method of inhibiting metal corrosion, in which the corrosivity of a reaction solution is adjusted and controlled by adding ozone into chemical agents or water that would contact with metal lead wires in the manufacturing process.

The method of inhibiting metal corrosion according to the present invention is applicable to a metal-containing substrate, which has a surface in contact with a reaction solution. The method includes the steps of mixing ozone (O₃) with the reaction solution and forming a passive metal oxide layer on the surface of the metal-containing substrate. The reaction solution added with ozone has an increased oxidizability. Since molecular ozone or free radical ozone is a very strong oxidizer, appropriate adjustment of ozone concentration in the reaction solution enables formation of a passive metal oxide layer on the metal surface to protect the metal beneath the passive layer against continuous oxidation or corrosion by the reaction solution.

The method of the present invention may further include the step of mixing the reaction solution with an additive, such as a suitable inorganic acid or any salt thereof, so as to adjust the oxidation-reduction property and the pH value of the reaction solution, in which the metal-containing substrate is disposed, and accordingly, change the corrosivity of the reaction solution and mitigate the metal corrosion tendency.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein

FIG. 1 is a flow chart showing the steps included in the method of inhibiting metal corrosion according to a preferred embodiment of the present invention; and

FIG. 2 is a potential-current polarization curve diagram.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method of inhibiting metal corrosion of the present invention is applicable to metal-containing substrate having a surface in contact with a reaction solution. The metal-containing substrate surface may be caused to contact with the reaction solution in different ways, such as immersing the metal-containing substrate in the reaction solution, or spraying the reaction solution on the metal-containing substrate. Please refer to FIG. 1 that is a flowchart showing the steps included in the method of inhibiting metal corrosion according to a preferred embodiment of the present invention. As shown, in a first step (110), ozone is mixed with the reaction solution. In a second step (120), a passive metal oxide layer is formed on the surface of the metal-containing substrate. And, in a third step (130), an adequate amount of additive is mixed with the reaction solution. In the step of mixing ozone with the reaction solution, either a solution containing ozone is added into the reaction solution, or gas-state ozone is directly added to dissolve in the reaction solution. The reaction solution may be ultrapure water for cleaning, deionized water, water solution containing acid/alkali additives, or etching liquid and photoresist remover being used in other related process. It is preferable the concentration of ozone in the reaction solution is within the range from 0.1 to 30 ppm.

The additive used in the preferred embodiment of the present invention may be an inorganic acid or any salt thereof, such as carbonic acid, phosphoric acid, nitric acid, boric acid, silicic acid, etc. To add the additive, either a solution of the inorganic acid or any salt thereof is added into the reaction solution, or the inorganic acid or any salt thereof is directly added to dissolve in the reaction solution. Alternatively, the additive may be mixed with a solution and the mixture is then added into the reaction solution. The additive may be added independently or in any combination with other additives. It is preferable a total concentration of the additive in the reaction solution is between 10⁻⁵ and 10⁻¹ mole (M).

For the purpose of more clearly describing the method of the present invention, an experiment is conducted. Five groups are included in the experiment. In the first group, only the deionized water is used as the reaction solution. In the second group, the deionized water is used as the reaction solution, into which ozone is added to reach an ozone concentration of 5 ppm and a pH value of 5.8. In the third group, the deionized water is used as the reaction solution, into which ozone and carbonic acid are added to reach an ozone concentration of 5 ppm and a pH value of 4.2. In the fourth group, the deionized water is used as the reaction solution, into which ozone and nitric acid are added to reach an ozone concentration of 5 ppm and a pH value of 3.5. In the fifth group, the deionized water is used as the reaction solution, into which ozone and phosphoric acid are added to reach an ozone concentration of 5 ppm and a pH value of 3.6. Values of corrosion potential (E_(corr)) and corrosion current (I_(corr)) of aluminum metal in the solution of the five groups are electrochemically measured. FIG. 2 is a potential-current polarization curve diagram showing the results from the above experiment. The values of corrosion potential and corrosion current of the aluminum metal in the solution of the five groups are derived based on FIG. 2, and indicated in the following Table 1. TABLE 1 I_(corr.) (A/cm²) E_(corr.) (V) 1^(st) group 3.611 × 10⁻⁸ −0.5739 2^(nd) group 5.135 × 10⁻⁸ −0.4798 3^(rd) group 1.652 × 10⁻⁸ 0.0236 4^(th) group 8.393 × 10⁻⁹ −0.2659 5^(th) group 1.745 × 10⁻⁸ −0.2478

A low corrosion potential represents the aluminum metal tends to be easily corroded in the reaction solution; and a high corrosion current represents the aluminum metal is more quickly corroded in the reaction solution. As can be seen from Table 1, the aluminum metal has the highest corrosion tendency in the first group. In the second to the fifth group, in which ozone is added into the reaction solution, the corrosion tendency of the aluminum metal is obviously decreased. In the third to the fifth group, in which inorganic acid, such as carbonic acid, nitric acid, or phosphoric acid, is added into the reaction solution, the corrosion potential of the aluminum metal is effectively increased. From the above results, it is found the reaction solution added with ozone shows significant corrosion inhibition effect in terms of metal, as compared with the reaction solution without adding ozone.

The present invention has been described with a preferred embodiment thereof and it is understood that many changes and modifications in the described embodiment can be carried out without departing from the scope and the spirit of the invention that is intended to be limited only by the appended claims. 

1. A method of inhibiting metal corrosion, said method being applicable to a metal-containing substrate that has a surface in contact with a reaction solution; said method comprising the steps of: mixing ozone with the reaction solution; and forming a passive metal oxide layer on the surface of the metal-containing substrate.
 2. The method of inhibiting metal corrosion as claimed in claim 1, wherein a concentration of the ozone in the reaction solution is preferably within the range from 0.1 to 30 ppm.
 3. The method of inhibiting metal corrosion as claimed in claim 1, wherein the ozone is dissolved in a solution before being added into the reaction solution.
 4. The method of inhibiting metal corrosion as claimed in claim 3, wherein the solution includes an additive.
 5. The method of inhibiting metal corrosion as claimed in claim 4, wherein the additive includes an inorganic acid or any salt thereof, or any combinations of the inorganic acid and any salt thereof.
 6. The method of inhibiting metal corrosion as claimed in claim 5, wherein the inorganic acid is selected from the group consisting of carbonic acid, phosphoric acid, nitric acid, boric acid, and silicic acid.
 7. The method of inhibiting metal corrosion as claimed in claim 5, wherein the additive in the reaction solution has a concentration preferably within the range from 10⁻⁵ to 10⁻¹M.
 8. The method of inhibiting metal corrosion as claimed in claim 1, wherein the ozone is in gas state and directly dissolved in the reaction solution.
 9. The method of inhibiting metal corrosion as claimed in claim 1, further comprising the step of mixing an additive with the reaction solution.
 10. The method of inhibiting metal corrosion as claimed in claim 9, wherein the additive includes an inorganic acid or any salt thereof, or any combinations of the inorganic acid and any salt thereof.
 11. The method of inhibiting metal corrosion as claimed in claim 10, wherein the inorganic acid is selected from the group consisting of carbonic acid, phosphoric acid, nitric acid, boric acid, and silicic acid.
 12. The method of inhibiting metal corrosion as claimed in claim 10, wherein the additive in the reaction solution has a concentration preferably within the range from 10⁵ to 10⁻¹M.
 13. The method of inhibiting metal corrosion as claimed in claim 1, wherein the reaction solution is selected from the group consisting of ultrapure water, deionized water, and water solution containing acid/alkali agent.
 14. The method of inhibiting metal corrosion as claimed in claim 1, wherein the reaction solution is selected from the group consisting of etching liquid and photoresist remover.
 15. The method of inhibiting metal corrosion as claimed in claim 1, wherein the metal-containing substrate is immersed in the reaction solution.
 16. The method of inhibiting metal corrosion as claimed in claim 1, wherein the reaction solution is sprayed on the metal-containing substrate.
 17. The method of inhibiting metal corrosion as claimed in claim 1, wherein the reaction solution is immersed the metal-containing substrate. 